Surfaces not being illuminated
All the walls etc. only have a glossy shader with 0 roughness. This means light will be reflected specularly, without being scattered. In other words, every surface is acting as a perfect mirror. 

See How do you make a lamp light up glossy surfaces? for a more detailed explanation of why this is a problem.

To fix this, try using a diffuse shader instead:



Though eventually you'll want to set up a mix of different shaders (probably a bit of both diffuse and glossy) with textures, etc.